ASoC: dt-bindings: Simplify port schema

ASoC: dt-bindings: Simplify port schema

The use of 'definitions' is not necessary and also problematic because the
dtschema tools don't process 'definitions' resulting in this spurious
warning:

Documentation/devicetree/bindings/sound/renesas,rsnd.example.dtb: sound@ec500000: port:endpoint: Unevaluated properties are not allowed ('phandle' was unexpected)
        from schema $id: http://devicetree.org/schemas/sound/renesas,rsnd.yaml#

Fix this by moving the port schema to #/properties/port and referencing
that directly from the 'ports' schema.

Really, a binding should just always use 'ports' if multiple ports are
possible. There's no benefit to supporting both forms. However, it appears
there are already lots of users of this one with a single 'port' node.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20231101140923.16344-2-robh@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>